I. Field of the Invention
This invention relates generally to punching apparatus and more particularly integrates a new concept for slitting thin film without producing waste material.
In the past few decades the packaging industry has widely adopted the polyethylene bags as a very inexpensive and practical alternative to more unexpedient methods of wrapping products. The contemporary use of plastic bags encompasses diverse products, some of which are: scientific apparatuses, garment products, and most importantly food. It is sometimes imperative that, when packaged in polyethylene bags, the products be properly ventilated.
II. Description of the Related Art
Customarily, ventilation is achieved by punching sizable holes in plastic bags, thus allowing air to circulate about the packaged goods. The aforesaid holes are punched by additional equipment, mounted on the frame of a bag-making machine and perforating synchronously with the operations of the latter. This kind of equipment, although having the advantage of integrating the perforating with the sealing and cutting processes, also has the shortcoming of producing waste material while cutting off some of the polyethylene to form the desired openings. Such machines are: U.S. Pat. No. 3,524,368 to Goldman (1970); U.S. Pat. No. 3,236,130 to Robert (1966). The inside parts of the holes are severed by a cutting device, and consequently have to be disposed of in many cumbersome ways. Furthermore, the severed parts of the holes frequently remain attached to the inside of the bag and are latter introduced into the packaged produce. Moreover, such punching devices are easily breakable and require sharpening of the cutting tools. The inconvenience of removing great quantities of waste plastic, the problems related to its lawful disposal, and the discomfort of having polyethylene residues in the packaged products have pushed the packaging industry to look for an alternative form of ventilation openings. The alternative is to stack a considerable number of finished but non-perforated bags from the bag-making machine and to place them on another machine, which would compress the stack and punch small slits into the polyethylene. This method of perforating ventilation slits eliminates most problems related to the undesired polyethylene residues, but considerably increases the time and cost of production. Indeed, with this method, the perforating is not integrated with the other bag-making manipulations, but is a distinct, costly, imprecise, and time-consuming process.
There is, therefore, a need for an auxiliary equipment that would be mounted on and would perforate synchronously with bag-making machines, piercing a desirable quantity of small ventilation slits without producing any residual waste material.